The present invention is a mechanical assembly, for regulating the temperature of an integrated circuit chip (IC-chip), having a gimbaled heat-exchanger with coiled spring conduits. This mechanical assembly has use in electromechanical systems that test IC-chips.
Today, a single state-of-the-art IC-chip can contain more than one-hundred-million transistors, and those transistors must be tested before the IC-chip is sold to a customer. Usually, each IC-chip is incorporated into an integrated circuit module (IC-module), and then the IC-chip in the IC-module is tested with a “burn-in” test, a “class” test, and a “system level” test. In one type of IC-module, the IC-chip is attached to a substrate and covered with a lid. In another type of IC-module, the IC-chip is attached to the substrate, but the IC-chip is not covered with any lid. In either case, electrical terminals are provided on the substrate which are connected by microscopic conductors in the substrate to the IC-chip.
The “burn-in” test thermally and electrically stresses the IC-chips to accelerate “infant mortality” failures. The stressing causes immediate failures that otherwise would occur during the first 10% of the IC-chips' life in the field, thereby insuring a more reliable product for the customer. The burn-in test can take many hours to perform, and the temperature of the IC-chip typically is held in the 90° C. to 140° C. range. Because the IC-chips are also subjected to higher than normal voltages, the power dissipation in the IC-chip can be significantly higher than in normal operation. This extra power dissipation makes the task of controlling the temperature of the IC-chip very difficult. Further, in order to minimize the time required for burn-in, it is also desirable to keep the temperature of the IC-chip as high as possible without damaging the IC-chip.
The “class” test usually follows the burn-in test. Here, the IC-chips are speed sorted and the basic function of each IC-chip is verified. During this test, power dissipation in the IC-chip can vary wildly as the IC-chip is sent a stream of test signals. Because the operation of an IC-chip slows down as the temperature of the IC-chip increases, very tight temperature control of the IC-chip is required throughout the class test. This insures that the speed at which the IC-chip operates is measured precisely at a specified temperature. If the IC-chip temperature is too high, the operation of the IC-chip will get a slower speed rating. Then the IC-chip will be sold as a lower priced part.
The “system level” test is the final test. Here, the IC-chips are exercised using software applications which are typical for a product that incorporates the IC-chips. In the system level test, the IC-chips are tested over a temperature range that can occur under normal operating conditions, i.e. approximately 20°-80° C.
In the '417 application, FIG. 1 shows an entire control system for maintaining the temperature of an IC-chip near a set-point while the above tests are performed. That FIG. 1 system includes an electric heater, an evaporator, an input conduit, and an output conduit, all of which are connected together to form one heat-exchanger. The present invention is a mechanical assembly which constitutes a novel physical implementation of the heat-exchanger.
For ease of reference, FIG. 1 of the '417 application is reproduced here as FIG. 1. Also, TABLE 1 from the '417 application, which identifies all of the components in FIG. 1, is reproduced below.
TABLE 1ComponentDescription20Component 20 is a thin,flat electric heater. Theheater 20 has one flat facewhich contacts the IC-chip10, and it has an oppositeflat face which isconnected directly tocomponent 21. Electricalpower PH is sent to theheater 20 on conductors20a. The temperature ofthe heater 20 is detectedby a sensor 20b in theheater 20. Thistemperature is indicated bya signal STH on conductors20c.21Component 21 is anevaporator for arefrigerant. Therefrigerant enters theevaporator 21 in a liquidstate through a conduit21a, and the refrigerantexits the evaporator 21 ina gas state through aconduit 21b. Thetemperature of theevaporator 21 is detectedby a sensor 21c on theexterior of the evaporator.This temperature isindicated by a signal STE onconductors 21d.22Component 22 is a valvewhich receives therefrigerant in a liquidstate from a conduit 22a,and which passes thatrefrigerant at a selectableflow rate to the conduit21a. The flow rate throughthe valve 22 is selected bya control signal SFV onconductors 22b. In oneembodiment, the signal SFVis a pulse modulatedsignal, and the valve 22opens for the duration ofeach pulse. In anotherembodiment, the signal SFVis an amplitude modulatedanalog signal, and thevalve 22 opens to a degreethat is proportional to theamplitude of the signal.23Component 23 is acompressor-condenser whichhas an input that isconnected to conduit 21b,and an output that isconnected to conduit 22a.The compressor-condenser 23receives the refrigerant inthe gas state, and thencompresses and condensesthat refrigerant to theliquid state.24Component 24 is a socketwhich holds the substrate11. Electrical conductors24a, 24b and 24c passthrough the socket to theIC-chip 10. The conductors24a carry test signals toand from the IC-chip 10.The conductors 24b carryelectrical power PC to theIC-chip 10. The conductors24c carry signals STC whichindicate the temperature ofthe IC-chip 10. Thesesignals STC are generated bya temperature sensor 10athat is integrated into theIC-chip 10.25Component 25 is a powersupply which sends thepower PH to the electricheater 20 with a selectablemagnitude. The amount ofpower that is sent at anyinstant is selected by asignal SPH on conductors25a.26Component 26 is a controlcircuit for the heaterpower supply 25. Thiscontrol circuit 26generates the signal SPH onthe conductors 25a inresponse to the signals STE,STH , STC, and SP which itreceives on the conductors21d, 20c, 24c and 26a. Thesignal SP indicates a set-point temperature at whichthe IC-chip 10 is to bemaintained. The controlcircuit 26, together withthe power supply 25 and theelectric heater 20, form afirst feedback loop in theFIG. 1 control system.This first feedback loopquickly compensates forchanges in powerdissipation in the IC-chip10 and thereby maintainsthe temperature of the IC-chip 10 near the set-point.27Component 27 is a controlcircuit for the valve 22.This control circuit 27generates the signal SFV onthe conductors 22b inresponse to the signals SPH,STE, and SP which itreceives on the conductors25a, 21d, and 26a. Thecontrol circuit 27,together with the valve 22and the evaporator 21, forma second feedback loop inthe FIG. 1 control system.This second feedback looppasses the liquidrefrigerant through theevaporator with a variableflow rate that reduces theoverall usage of electricalpower in the FIG. 1 system.
In the '417 application, the invention focuses on the first and second feedback loops which are identified in TABLE 1 under components 26 and 27. With those two feedback loops, the temperature of the IC-chip is maintained near the set-point, and the overall power usage in the FIG. 1 system is greatly reduced. This is achieved independently of any particular physical implementation of the heat-exchanger components 20, 21, 21a, and 21b.
By comparison, the present invention focuses entirely on a physical implementation for the heat-exchanger components 20, 21, 21a, and 21b. With this physical implementation, certain interface problems are avoided which can occur at the pressed joint between the electric heater 20 and the IC-chip 10. These interface problems are described herein in the BRIEF SUMMARY OF THE INVENTION and the DETAILED DESCRIPTION.
Accordingly, a primary object of the present invention is to provide a mechanical assembly, which is a heat-exchanger for controlling the temperature of an IC-chip, having a novel physical structure which overcomes the above interface problems.